Alterations in adrenergic receptor responsiveness in man may be important in the pathogenesis and maintenance of the hypertensive state and in cardiovascular regulation in the elderly. The proposed studies will attempt to elucidate the alterations in alpha- and beta-receptor responsiveness in hypertensive subjects and beta-receptor responsiveness in the elderly. Assays of alpha 1 and beta 2 adrenergic receptor properties on circulating cells will be correlated with determination venous adrenergic responsiveness. The mechanism by which dietary sodium modulates beta-adrenergic responsiveness in hypertension will also be explored. Further, whether a low sodium diet corrects the defect in beta-adrenergic responsiveness in the elderly will be determined. To identify the site of the defect in lymphocyte beta-adrenergic receptor responsiveness in hypertensive and elderly subjects, possible alterations in beta-receptor structure and Gs structure/density will be monitored. Altogether this proposal outlines an integrated approach to the study of altered human adrenergic receptor function in hypertension and aging and may help determine the importance of proposed in vitro biochemical mechanisms in in vivo human adrenergic receptor regulation.